Excessive airway narrowing is an important cause of breathing difficulties in airway diseases such as asthma. Airway smooth muscle (ASM) mechanics is an important determinant of airway diameter and resistance. Recent findings indicate that actin cytoskeletal remodeling is a new cellular process in ASM that can regulate ASM mechanics. This proposal investigates how G-protein coupled receptor (GPCR) activation and mechanical deformation interactively regulate cytoskeletal recruitment of actin- and integrin-binding proteins in differentiated ASM using multiple approaches ranging from molecular biology to muscle mechanics. GPCR activation is physiologically relevant because ASM cells in vivo are exposed to GPCR agonists such as acetylcholine released from parasympathetic nerves and histamine released from mast cells during airway inflammation. Mechanical deformation is physiologically relevant because ASM cells undergo constant lengthening and shortening during normal breathing cycles. Furthermore, this proposal will determine whether force development or dynamic stiffness is the regulated variable of cytoskeletal recruitment. Specific aim 1 tests the hypothesis that GPCR-mediated cytoskeletal recruitment of actin- and integrin-binding proteins is receptor-specific, temporally ordered, signaled by RhoA, Erk1/2 MAPK, and p38 MAPK, regulated by alpha-actinin, and important for the regulation of dynamic stiffness. Results from specific aim 1 will provide new information on the temporal dynamics, signaling pathways, and function of GPCR-mediated cytoskeletal recruitment process in differentiated ASM. Specific aim 2 tests the hypothesis that steady-state and past history of mechanical strain modulate GPCR-mediated cytoskeletal recruitment of actin- and integrin-binding proteins by modulating the activation of RhoA, Erk1/2 MAPK, and p38 MAPK. Results from specific aim 2 will provide new information on how differentiated ASM adapts to mechanical deformation by remodeling the actin cytoskeleton. Relevance to Public Health: Excessive airway narrowing is an important problem of airway diseases such as asthma. This proposal investigates a new cellular mechanism of airway smooth muscle (cytoskeletal recruitment) that may contribute to airway narrowing in asthma. Understanding the basic science of this cellular mechanism may lead to new methods for the treatment of airway diseases such as asthma.